The studies envisioned in this proposal deal with the development and regeneration of the peripheral nervous system, using two different insect species as experimental material because of the technical advantages which they offer. Our principal goals are as follows: (1) To evaluate the role of early differentiating (pioneer) neurons in the establishment of peripheral neural pathways, both during normal development and during the regeneration of appendages. (2) To examine the role of impulse activity and transmitter metabolism in these processes. (3) To examine by means of immunological probes the role of cell surfaces in these processes, with special attention to the role of glial cells. (4) When suitable opportunities arise, to assess the role of these several factors in the establishment of central pathways and connections. In the fruitfly, Drosophila melanogaster, we will take advantage of suitable mutants and of sophisticated techniques for creating genetic mosaics to approach goals 1, 2 and 4. Specifically, we will be able to eliminate pioneer neurons, impulse activity and transmitter synthesis and degradation in selected regions of the body, and thus to assess their role in the establishment of neural pathways. In the house cricket, Acheta domesticus, a larger animal for which a great deal is already known about neural development and especially regeneration, we can approach goals 1, 3 and 4. We will be able to test the role of pioneer neurons by eliminating them with laser microsurgery. We propose to develop immunological markers for glial cells and to use these in the study of the origin of glia and its role in neural development and regeneration. The recent literature indicates a strong convergence of results and interpretations from studies on a variety of animal species used in the field of neural development. We expect that careful analyses of the roles of pioneer neurons, glial cells, impulse activity and transmitter biochemistry in the establishment and regeneration of neural pathways will be of broad interest to developmental neurobiologists, including those with strong clinical interests.